Ultrasonic signals are applied to the top of rails from moving vehicles. The ultrasonic energy travels from the top of the rail to its base. An echo indicates a flaw as the energy passes down through the rail. When the energy reaches the base a very strong echo is returned to the top of the rail for detection by the test apparatus which originally sent the ultrasonic signal into the top of the rail. In order to measure the precise moment that a return echo is received corresponding to the base of the rail, a time pulse is generated, corresponding to the generation of the ultrasonic signal and the return of the echo through the known depth of the rail. A strong echo at any precise moment on the time pulse indicates a flaw has occurred in the rail.
In summary then, with the depth of a rail known in advance timed pulses can be produced which correspond to the base echo. A loss of base echo at the precise time of the timing pulse predicts a strong evidence of a flaw or abnormality which requires very careful investigation of that rail in order to avoid a rail failure and its ultimate catastrophe.
The prior art utilizing this equipment has been very effective; however, rail thickness or depths vary considerably from rail bed to rail bed. When a rail change occurs, prior art ultrasonic generator and detector mechanisms must be recalibrated by adjusting the time pulse to correspond to the new rail thickness which requires stopping and adjusting the equipment.
The present invention completely automates ultrasonic testing of rails in that it provides an automatic method and means for measuring the thickness of the rail so that a base gate can be produced automatically corresponding to different rail thickness.